Chris Collins discusses a single-handed draw and the importance of why you must draw with one hand. Although, a two handed draw to clear a garment and draw a gun from concealment is a good skill to have, every shooter should invest a certain amount of time training a single-handed draw.
You might ask, “Am I training too many different skill sets which might confuse my body in a critical incident?” This is a valid question where in general, you don’t want to train two different skills for one task based on a stimulus. In this case the stimulus is a need to draw a gun and the two different mechanical tasks are a two-handed draw and a one-handed draw. However, if your support hand is occupied and you must draw the gun, you may find that you will naturally draw the gun with one hand if you have a sufficient number of training reps with a single-handed draw from concealment.
As Chris describes above, your support hand may be over your head covering your skull from receiving deadly blows from a lethal threat. This is a classic case where you want to have some training and repetitions in drawing your pistol from the appendix or four o’clock carry to reasonably defend yourself.